Growing plants from corms offers a rewarding experience, transforming small, unassuming structures into vibrant blooms and lush foliage. These specialized plant parts hold the promise of new life, making gardening accessible and enjoyable for many. This guide provides clear, concise information on understanding corms, planting them correctly, and providing ongoing care for successful growth.
What Are Corms
Corms are often mistaken for bulbs, but they possess distinct botanical differences. A corm is a swollen, underground stem that functions as a storage organ, accumulating nutrients to sustain growth during dormancy. Unlike true bulbs, which consist of layers of fleshy, modified leaves, a corm is solid internally. If cut in half, a corm would appear uniformly solid, whereas a bulb would reveal concentric rings of scales.
Roots typically emerge from the basal plate at the bottom of the corm, while shoots and new growth develop from buds located on the top or sides. As the plant grows and flowers, the stored nutrients in the parent corm are utilized, causing it to shrivel and often die back. However, new corms, sometimes called cormels or cormlets, form on top of or around the base of the old corm, ensuring the plant’s regeneration for the following season. Common garden plants that grow from corms include gladiolus, crocus, freesia, cyclamen, and some varieties of iris.
Getting Ready to Plant
Careful preparation is key for successful corm planting. Select firm corms free from mold, rot, or significant damage. Healthy corms are more likely to sprout vigorously and establish strong root systems.
The optimal planting time depends on the corm type and your local climate. Spring-planted corms, such as gladiolus and freesia, are typically placed in the ground after the last frost when soil temperatures have warmed, usually in early to mid-spring. Fall-planted corms, like crocuses, should be planted in early to mid-autumn, allowing them time to establish roots before the ground freezes for winter dormancy and spring blooming.
Site preparation is also important. Choose a location with ample sunlight, ideally six to eight hours daily. Well-draining soil is crucial to prevent waterlogging, which can lead to corm rot. If your soil is heavy clay, amend it with organic matter like compost, well-rotted manure, or sand to improve drainage and aeration, fostering healthy root development.
How to Plant Corms
Once corms and the planting site are ready, attention to detail is required. The general guideline for planting depth is to bury the corm two to three times its height; for example, a 1-inch tall corm would be planted 2-3 inches deep. This depth helps maintain consistent soil moisture, stabilizes soil temperature, and provides adequate protection from environmental extremes and potential pests.
Proper spacing between corms is essential to allow for adequate air circulation and nutrient uptake as the plants mature. A common recommendation is to space corms about 4 to 6 inches apart, although specific plant varieties may have slightly different requirements. For instance, saffron crocuses can be planted 2-3 inches apart. Correctly orienting the corm is another important step; typically, the pointed or slightly concave side, where new growth emerges, should face upward. The flatter or more rounded base, where roots will develop, should be placed facing down into the soil.
After placing the corms at the correct depth and orientation, gently backfill the holes with the prepared soil, ensuring the corms are fully covered. Lightly pat the soil to remove any large air pockets. After planting, water thoroughly to settle the soil and encourage root growth.
After Planting Care
Consistent care after planting is essential for healthy establishment and sustained growth. After the initial watering, ongoing moisture management is key; regular watering is necessary, especially during dry periods, but avoid overwatering, which can lead to rot. Aim for consistently moist, but not waterlogged, soil, particularly during active growth and flowering. Many plants from corms, such as gladiolus, benefit from about 1 inch of water per week, either from rainfall or irrigation.
Regarding fertilization, a balanced approach supports robust growth without encouraging excessive foliage at the expense of blooms. Incorporating compost or a slow-release granular fertilizer into the soil at planting provides a good foundation. Additional feeding can be done during the growing season, perhaps a month after planting and again when flower stalks begin to form, using a balanced all-purpose plant food. Monitor plants for signs of common pests like aphids or diseases such as fungal spots, addressing any issues promptly with appropriate organic or chemical treatments.
For tender corms in colder climates, such as many gladiolus varieties, overwintering often involves lifting them from the ground before the first hard frost. After digging, allow the corms to dry and cure in a warm, well-ventilated area for a few weeks, then remove excess soil and trim the stems. Store them in a cool, dark, and dry place with good air circulation, typically in mesh bags or cardboard boxes, at temperatures between 40-50°F (4-10°C) until the following spring.